Try each of these steps (preferably in order) to see if it helps resolve your problems...
1. Take out the SD card.
A. Remove the back cover of the phone, starting from the slot located at the lower left.
B. Remove the battery.
C. Remove the SD card.
D. Reinsert the battery.
E. Press and hold the Power key to turn your phone back on.
2. Check to see if your phone is running low on memory.
3. Clear app caches.
A. Clear the 'Cache' of your apps to free up space.
B. Be sure you clear only the apps cache and not the apps data.
NOTE: Make sure you save any information that could be lost in doing this. Like history, URLs, passwords, etc. that are associated with the app you are clearing the cache of.
C. From the home screen, swipe down the Status bar.
D. Tap the Settings icon.
E. From the General tab, scroll to and tap Apps.
F. Scroll to and tap the app.
G. Tap Storage.
H. Tap Clear cache.
4. Close or uninstall apps.
Some apps keep running in the background, even when you are not using them. Also, some apps consume more energy than others. Sadly some apps come pre-installed on your phone and you can't uninstall them.
A. From the home screen, swipe down the Status bar.
B. Tap the Settings icon.
C. From the General tab, scroll to and tap Apps.
D. Scroll to and tap the app.
E. Close (turn off) an app: Tap Force stop.
F. Uninstall (remove from phone) an app: Tap Uninstall, and then OK.
5. Update your phones Firmware.
If the phone is running out of date firmware this can also lead to problems. Make sure yours is up to date.